📚 Year 7 Cambridge Science: Common Misconceptions and How to Fix Them | 剑桥7年级科学：常见误区与纠正方法
Starting secondary science is exciting, but many students hold ideas about the natural world that do not quite match the scientific view. These misconceptions can be stubborn – they often come from everyday language or half‑remembered facts. In Year 7 Cambridge Science, spotting and fixing these misunderstandings early makes later topics much easier. This article takes ten of the most common misconceptions across biology, chemistry and physics, explains why they are wrong, and shows you exactly how to put them right.
开始中学科学学习是一件令人兴奋的事，但许多学生对自然世界的看法与科学观点并不完全一致。这些误区往往来自日常用语或一知半解，而且很难纠正。在剑桥7年级科学课程中，尽早发现并修正这些误解，会让后面的学习轻松很多。本文选取了生物、化学和物理领域十个最常见的误区，解释它们错在哪里，并告诉你正确的理解方法。
1. Breathing vs. Respiration | 呼吸与呼吸作用的混淆
One of the biggest mix‑ups is thinking that ‘breathing’ and ‘respiration’ mean the same thing. In biology, breathing (ventilation) is the physical process of moving air into and out of the lungs. Respiration, on the other hand, is a chemical reaction that happens inside every living cell. It uses glucose and oxygen to release energy, producing carbon dioxide and water as waste products.
最大的混淆之一是认为“呼吸”（breathing）和“呼吸作用”（respiration）是同一回事。在生物学中，呼吸（换气）是将空气吸入和排出肺部的物理过程。而呼吸作用是在每个活细胞中发生的化学反应，它利用葡萄糖和氧气释放能量，并产生二氧化碳和水作为废物。
To remember the difference, think of breathing as the delivery service that brings oxygen into the blood and removes carbon dioxide. Respiration is what the cells do with that oxygen. The word equation for aerobic respiration is:
要记住两者的区别，可以把呼吸想象成快递服务，负责把氧气送进血液并带走二氧化碳。呼吸作用则是细胞利用氧气做的事情。有氧呼吸的文字方程式为：
glucose + oxygen → carbon dioxide + water (+ energy released)
It is respiration that releases energy for movement, growth and keeping warm – not breathing itself.
正是呼吸作用释放能量用于运动、生长和保持体温——而不是呼吸本身。
2. Photosynthesis Only Happens During the Day | 光合作用只在白天进行
Many students believe that as soon as the sun sets, photosynthesis stops and the plant ‘goes to sleep’. It is true that the light‑dependent stage of photosynthesis requires sunlight, so the process of making glucose only occurs in the light. However, plants are still alive at night – they just switch to using the stored glucose for energy through respiration. Respiration goes on 24 hours a day in plant cells, just as it does in animal cells.
许多学生认为太阳一落山，光合作用就停止了，植物就“睡觉”了。的确，光合作用的光反应阶段需要阳光，因此制造葡萄糖的过程只在有光时进行。然而，植物在夜间仍然是活着的——它们只是转而利用储存的葡萄糖通过呼吸作用来获取能量。植物的呼吸作用和动物细胞一样，全天24小时都在进行。
A helpful way to think about it is that during the day, photosynthesis often produces more oxygen than respiration uses, so the plant appears to be giving out oxygen. At night, no photosynthesis occurs, so the net gas exchange is oxygen in and carbon dioxide out. The plant never stops respiring.
一个有用的理解方式是：白天，光合作用通常会产生比呼吸作用消耗的更多的氧气，因此植物看起来在释放氧气。到了晚上，没有光合作用，净气体交换就变为吸收氧气、放出二氧化碳。植物从未停止呼吸作用。
3. Plants Get Food from the Soil | 植物从土壤中获取食物
If you ask a young learner where a plant’s food comes from, they often answer ‘from the soil’ or ‘from the roots’. This is a very common idea, but it misses the fact that plants are producers – they make their own food by photosynthesis. Roots absorb water and dissolved mineral ions (like nitrates and magnesium), not food. The glucose produced in the leaves is the plant’s true food.
如果你问一个低年级学生植物的食物从哪来，他们常常回答“从土壤里”或“从根里”。这是一个非常普遍的想法，但它忽略了植物是生产者——它们通过光合作用制造自己的食物。根系吸收的是水分和溶解的矿物离子（如硝酸盐和镁离子），而不是食物。叶子里制造的葡萄糖才是植物真正的食物。
Mineral ions are used to build proteins and chlorophyll, but they do not provide energy. Only the glucose made in photosynthesis powers the plant’s activities. Understanding this helps students later when they study food chains and realise that plants are always at the start.
矿物离子用来制造蛋白质和叶绿素，但它们不提供能量。只有光合作用制造的葡萄糖才为植物的生命活动提供动力。理解这一点有助于学生今后学习食物链，并认识到植物总处在起点位置。
4. Heavier Objects Fall Faster | 物体越重下落越快
Our everyday experience with feathers and stones suggests that heavy things fall more quickly. This misconception goes back to ancient Greek ideas, but it was overturned by Galileo’s experiments. In the absence of air resistance, all objects fall at the same rate regardless of their mass. The famous demonstration – dropping a hammer and a feather on the Moon, where there is no air – showed they hit the ground together.
我们日常看到羽毛和石头的落地情况，会让人觉得重物落得更快。这种误解可以追溯到古希腊的观念，但被伽利略的实验推翻了。在没有空气阻力的情况下，所有物体无论质量大小都以相同的速率下落。著名的月球实验——在没有空气的月球上同时丢下锤子和羽毛——显示它们一起落到了地面。
On Earth, air resistance pushes against falling objects and affects lighter, larger‑surface‑area objects more. That is why a sheet of paper flutters down slowly while a crumpled‑up ball of the same paper drops quickly. The force of gravity on each kilogram is the same (about 9.8 N/kg). So in Year 7, remember: without air, everything accelerates at the same rate.
在地球上，空气阻力会阻碍下落物体，且对质量轻、表面积大的物体影响更大。这就是为什么一张平展的纸飘落得很慢，而同一张纸揉成团后会快速下落。每千克物体受到的重力是相同的（约9.8 N/kg）。所以7年级的同学请记住：没有空气时，所有物体都以相同的加速度下落。
5. Mass and Weight Are the Same | 质量与重量是一回事
In everyday language we often say ‘how much do you weigh?’ and give the answer in kilograms. In physics, though, mass and weight are not the same. Mass is the amount of matter in an object and is measured in kilograms (kg). Weight is the force of gravity acting on that mass and is measured in newtons (N). Your mass stays the same wherever you are; your weight changes if gravity changes.
在日常用语中，我们经常问“你体重多少？”并用千克回答。但在物理中，质量和重量并不是一回事。质量是物体所含物质的多少，单位是千克（kg）。重量是重力作用在该质量上的力，单位是牛顿（N）。无论你到哪儿，你的质量都保持不变；但如果重力改变，你的重量就会变。
The table below summarises the key differences.
下表总结了关键区别。
| Property | Mass | Weight |
|---|---|---|
| Definition | Amount of matter | Force of gravity on the mass |
| Unit | kilogram (kg) | newton (N) |
| Measured with | Balance | Newton meter / spring balance |
| Depends on location? | No – constant everywhere | Yes – varies with gravity |
On Earth, weight (N) = mass (kg) × gravitational field strength (N/kg). Since 1 kg has a weight of about 10 N on Earth, a 50 kg student has a weight of about 500 N. On the Moon, gravity is about 1.6 N/kg, so the same student would weigh only about 80 N – but their mass would still be 50 kg.
在地球上，重量（N）= 质量（kg）× 引力场强度（N/kg）。由于地球上1 kg物体的重量约为10 N，一名50 kg的学生重量约为500 N。月球上的引力场强度约为1.6 N/kg，因此同一名学生在那儿重量只有约80 N——但他的质量仍然是50 kg。
6. Current Gets Used Up in a Circuit | 电流在电路中消耗
A very common electrical misconception is that electric current is like fuel – it gets ‘used up’ as it goes around a circuit, so the current leaving a bulb is smaller than the current entering it. In a simple series circuit, however, the current is the same at all points. It is the energy carried by the charges that is transferred to the components, not the charges themselves being consumed.
电学中一个极为常见的误区是认为电流像燃料一样——沿着电路移动时会被“用掉”，因此离开灯泡的电流比进入灯泡的电流小。然而在简单的串联电路中，各点的电流是相同的。被消耗的是电荷携带的能量，而不是电荷本身被消耗。
Consider a model: imagine a train of coal trucks on a circular track. The coal (energy) is unloaded at the power station (bulb), but the trucks (charges) keep moving around the loop. Current is the flow rate of these trucks, which stays constant unless there is a branch. This explains why an ammeter placed anywhere in a single‑loop series circuit gives the same reading.
想象一个模型：一列煤车在环形轨道上行驶。在发电站（灯泡）处卸下煤炭（能量），但货车本身（电荷）继续在环上移动。电流是这些货车的流动速率，除非有支路，否则保持不变。这就解释了为什么把电流表放在单回路串联电路中的任何位置，读数都相同。
7. Melting and Dissolving Are the Same Process | 融化与溶解相同
Students often confuse melting and dissolving because both processes make a solid ‘disappear’ into a liquid. Melting is a change of state – a solid turns into a liquid when heated to its melting point, and the substance remains chemically the same. Dissolving, however, happens when a solid mixes with a liquid (the solvent) to form a solution, breaking into particles that are too small to see. The solid does not need to be heated to melt; it simply spreads out.
学生经常把融化与溶解混为一谈，因为这两个过程都会使固体“消失”在液体中。融化是一种状态变化——固体加热到熔点后变成液体，物质本身化学性质不变。而溶解是固体与液体（溶剂）混合形成溶液，固体分裂成肉眼看不见的微粒。固体不需要被加热融化；它只是分散开来。
When ice melts, the water particles gain energy, overcome some of the forces holding them in fixed positions, and become liquid water. When sugar dissolves in tea, the sugar particles separate and disperse between the water particles. Filtration can separate undissolved solid from a liquid, but dissolved substances pass through the filter paper – a clear sign the processes are different.
冰融化时，水粒子获得能量，克服了部分固定位置上束缚它们的力，变成液态水。糖溶解在茶里时，糖粒子分开并分散到水粒子之间。过滤可以将未溶解的固体与液体分开，但溶解的物质会穿过滤纸——这清楚地表明两种过程是不同的。
8. Bubbles in Boiling Water Are Made of Air | 沸腾时气泡里是空气
When you watch a pan of water heat up, you see bubbles rising from the bottom. Many pupils confidently say the bubbles contain ‘air’ or ‘oxygen’. In fact, they are filled with water vapour – the gaseous state of water. As the water near the heat source exceeds 100 °C, liquid water changes to gas, forming bubbles that rise and escape. These bubbles grow because more water vaporises into them on the way up.
当你观察一锅加热的水时，会看到气泡从底部升起。很多学生自信地说这些气泡里是“空气”或“氧气”。实际上，气泡里充满了水蒸气——即气态的水。当靠近热源的水温超过100°C时，液态水变成气态，形成气泡并上升逸出。这些气泡在上升的过程中因更多水汽化进入而变大。
The fact that the bubbles can form only when the liquid water reaches its boiling point supports this explanation. If they were air, we would expect bubbles at any temperature. Also, when the steam hits a cool surface, it condenses back into tiny drops of water, showing that the gas was indeed water vapour.
气泡只有在液态水达到沸点时才能形成这一事实支持了上述解释。如果气泡里是空气，那任何温度下都应该有气泡。而且，当水蒸气碰到冷的表面时会凝结回小水滴，这说明该气体确实是水蒸气。
9. No Forces Act on a Stationary Object | 静止物体没有力作用
It is easy to think that if something is not moving, no forces are acting on it. Newton’s First Law tells us a different story: an object remains at rest or moves at constant speed only if the forces on it are balanced (or absent). A book sitting on a table has two main forces acting on it – gravity pulling it downwards and the normal contact force from the table pushing it upwards. These forces are equal in size and opposite in direction, so the net force is zero.
人们容易认为，如果某物静止不动，就没有力作用在它上面。牛顿第一定律告诉我们一个不同的故事：物体保持静止或匀速直线运动，必须满足作用在它上面的力相互平衡（或没有力）的条件。放在桌上的一本书就受到两个主要的力——重力向下拉它，桌面对它的支持力向上推它。这两个力大小相等、方向相反，因此合力为零。
The same principle applies to a hanging picture, a floating boat or a standing student. In each case, forces are acting, but they cancel out. Recognising balanced forces is a foundational skill for understanding more complex motion and for drawing accurate force diagrams in later years.
同样的原理也适用于挂在墙上的画、漂浮的船或站立的学生。每种情况都有力在作用，只是它们互相抵消了。识别平衡力是为今后理解更复杂运动和绘制正确的受力图打基础的技能。
10. Mitochondria Produce Energy | 线粒体产生能量
Textbooks and teachers often say ‘mitochondria are the powerhouses of the cell’, which can lead to the idea that mitochondria create energy. In science, energy cannot be created or destroyed – it can only be transferred or transformed. Mitochondria are the sites of aerobic respiration, where the chemical energy stored in food molecules (mainly glucose) is transferred to a molecule called ATP, which cells can use directly.
教科书和老师常说“线粒体是细胞的能量工厂”，这可能导致学生认为线粒体创造了能量。科学上，能量既不能被创造也不能被消灭——只能被转移或转化。线粒体是有氧呼吸的场所，储存在食物分子（主要是葡萄糖）中的化学能在这里被转移到一种叫做ATP的分子中，供细胞直接使用。
The overall process in mitochondria can be summarised as:
线粒体中的整个过程可以总结为：
glucose + oxygen → carbon dioxide + water, and energy is transferred to ATP
It is more accurate to say ‘mitochondria transfer energy from glucose to ATP’ rather than ‘mitochondria produce energy’. This careful wording aligns with the conservation of energy principle and prevents deeper confusion in later biology and physics.
更准确的说法是“线粒体将葡萄糖中的能量转移到ATP”，而不是“线粒体产生能量”。这种严谨的表述符合能量守恒原理，并防止以后学习生物和物理时产生更大的混淆。
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